May have spoken too quickly Tailmaker JUST masked/goggled up, and took my least used full sintered shape which was a solid sintered diamond truncated cone.Grabbed a damaged selenite crystal specimen(Mohs 2), and a non-nacreous shard of oyster shell(approx. Mohs 3), and ran Foredom at max 18K and tried to approximate 1 IPM.Spent about 5 minutes using just the shank side corner, and after rinsing with water, under my 10X loupe, I couldn't see deformation of the corner or break down of the diamond.Sooo.....may be worth an experiment? (at YOUR cost:)

For me, I LIKE Randall's results with using old carbide bits

DO know that I drilled 200 holes in oyster shells for my Mom last Christmas for ornaments,and would up with Drillman1's .0625" downcut carbide in the Foredom at about 16K after trying several different bits, and drilled wet by method of putting a sponge in rubbermaid container and pressing shell down until barely covered to avoid dust.